1. Field of the Invention
The present invention relates to a method for processing a silicon substrate in which a minute structure is formed on a surface of the silicon substrate.
2. Description of the Related Art
In a photoelectric conversion device such as a solar cell formed using a silicon substrate, a structure in which minute unevenness is formed on a light-receiving surface, which is also referred to as a texture structure, is often used. On the surface processed to have unevenness, multiply-reflected light is incident, and the light obliquely propagates into a photoelectric conversion region; thus, the light pass length is increased. Further, a light trapping effect in which reflected light by a back electrode or the like of light propagated into the photoelectric conversion region is totally reflected at the surface can occur, and thus the electric characteristics of the photoelectric conversion device can be greatly improved.
As a method for forming such unevenness on a surface of a silicon substrate, a method in which a single crystal silicon substrate is anisotropically etched using an alkaline solution to form pyramid-shaped unevenness is known. Note that the method utilizes a difference in etching rates among plane orientations and is not suitable for a polycrystalline silicon substrate whose plane orientation is random on a surface of the substrate.
Further, a method in which a metal is deposited on a surface of a silicon substrate in a mixture solution containing a metal ion, oxidizer, and hydrofluoric acid to make the surface of the silicon substrate porous by utilizing the catalytic action of the metal and to form unevenness is disclosed in Patent Document 1.
Further, as a similar method, a method in which metal particles are deposited on a surface of a silicon substrate having unevenness in a plating solution to make the surface of the silicon substrate porous in a mixture solution containing oxidizer and hydrofluoric acid and to form unevenness is disclosed in Patent Document 2.